1. Field of the Invention
The present invention relates a press-forming apparatus for subjecting a material to a press-forming to provide a heat transfer member for a heat exchanger, and particularly to such an apparatus which permits formation of a plurality of press-formed portions as aligned on the material through the press-forming steps utilizing a plurality of forming sections.
2. Description of the Related Art
If there is a wish that heat transfer coefficient is increased to enhance heat exchange effectiveness, utilizing a heat exchanger by which heat exchange is made between a high temperature fluid and a low temperature fluid, a plate-type heat exchanger has conventionally been used widely. The plate-type heat exchanger has a structure in which a plurality of heat transfer members having a plate-shape are placed in parallel to one upon another at prescribed intervals so as to form passages, which are separated by means of the respective heat transfer member. A high temperature fluid and a low temperature fluid flow alternately in the above-mentioned passages to provide a heat exchange through the respective heat transfer members.
In general, the heat transfer member used in the conventional plate-type heat exchanger has a predetermined pattern of corrugations, which serves as a heat transfer face having the opposite surfaces with which heat exchange fluids are to come into contact. Such a pattern of corrugations causes turbulence in the fluids to improve the heat transfer efficiency, increases the heat transfer area and enhances the strength of the plate.
The heat transfer member having such a pattern of corrugations is generally formed of a metallic sheet. The metallic sheet is press-formed into a prescribed shape, thus providing a finished product, which is to be put into practice. The conventional press-forming apparatus utilizes a pair of metallic dies. More specifically, the material to be press-formed is held between the dies. Moving the dies closely to each other causes formation of a pattern of corrugations serving as the heat transfer face and the other press-formed portions on the metallic thin sheet of the material to be press-formed.
The press-forming operation for the heat transfer member has conventionally been carried out in this manner. The pair of dies forms the pattern of irregularities of the whole heat transfer member. It is therefore impossible to form any pattern of corrugations having a size larger than the molds. As a result, there is a restriction that the size of the heat transfer member depends on the size of the dies, thus making it impossible to manufacture the heat transfer member having a large area, due to limitation of the size of the dies.
In addition, the dies of the press-forming apparatus give the material to be press-formed a various kind of corrugations. When the pitch of the pattern of corrugations is not uniform so that the pitch on the one end side is small, but the pitch on the other side is large, conditions in the drawing of the material from the non-pressed portion to the pressed portion are different in the respective patterns of corrugations. A serious residual strain occurs in the press-formed portion and the non-pressed portion of the heat transfer member after completion of the press-forming step. As a result, the heat transfer member may curve partially or over the entirety, or be deformed, thus causing problems.